Physicists from the University of Queensland were able to simulate time travel by looking at the behavior of a photon as it passes through a wormhole and interacts with an “older” version of itself.

This study, which was published in Nature Communications, hopes to look at the possibility of time travel at a quantum level and to unify Einstein’s theory of relativity with quantum mechanics—one of the holy grails of modern physics.

Einstein’s theory of relativity and quantum mechanics both present the possibility of time travel. However, there is a gap between these theories because of their scale and scope. Quantum mechanics explains the interactions between atoms and particles, whereas Einstein’s theory of relativity explains the interactions between galaxies and stars.

Paradoxes: The problem with time travel

According to Einstein’s theory, it’s possible to travel back in time through a closed timelike curve, more commonly known as a “wormhole”. But scientists struggle with this theory because of the paradoxes that it presents. The most popular time travel paradox, the grandfather paradox, presents a scenario where a time traveler goes back in time and prevents his grandparents from ever meeting, basically preventing the traveler from ever existing.

But in 1991, it was predicted that these paradoxes could be avoided if time travel is done in the quantum world. Because of the famous Heisenberg Uncertainty Principle, the properties of quantum particles are “fuzzy” and “uncertain,” providing enough flexibility to avoid the paradoxes.Time travel through the quantum world is also much more feasible because the quantum model of a closed timelike curve can be formulated with consistently with relativity

Sliding down the (worm)hole

PhD student Martin Ringbauer, Physics professor Tim Ralph, and their team at the University of Queensland’s School of Physics and Mathematics explored these properties by creating a mathematical equivalence between two cases.

Ringbauer explains: “In the first case, photon one ‘travels’ through a wormhole into the past, then interacts with its older version. And in the second case, photon two travels through normal space-time, but interacts with another photon that is trapped inside a closed timelike curve forever.”

“We used single photons to do this,” said UQ Physics Professor Tim Ralph, “but the time-travel was simulated by using a second photon to play the part of the past incarnation of the time travelling photon.”

Quantum time travel

Sure, the experiment won’t make it possible for you to travel to ancient Egypt for your vacation in the near future. But the simulation did present significant insights on how light travels through time and the behavior of quantum molecules.

“We see in our simulation (as was predicted in 1991) how many effects become possible, which are forbidden in standard quantum mechanics,” Ringbauer explained.

“For example it is possible to perfectly distinguish different states of a quantum system, which are usually only partially distinguishable. This makes quantum cryptography breakable and violates Heisenberg’s uncertainty principle. We also show that photons behave differently, depending on how they were created in the first place.”

As for the possibility of time travel in the future, we may have to wait a while.

“Our study provides insights into where and how nature might behave differently from what our theories predict,” says Ralph.
Although the laws of standard quantum mechanics so far seem to be pretty consistent in nature, Ralph says that there is a need to test this simulation in different environments, such as near black holes, where the extreme effects of relativity may have an impact.